1. Field of the Invention
The present invention relates to control of air throttling through an engine using a combination of plenum and secondary throttles and low and high speed intake runners.
2. Disclosure Information
Secondary throttles located adjacent internal combustion engine intake ports are known to produce improved combustion stability, particularly at idle, as compared with conventional plenum throttle arrangements. This is particularly true with engines having large amounts of overlap between the intake and exhaust events. Improvement in idle stability and off-idle and light load combustion stability arises from the fact that the individual cylinder secondary throttles, which are also termed "load control port throttles," control the backflow of residual exhaust gas into the intake port during the overlap period, while allowing freer flow at high load, high RPM operation when the secondary throttles are open. Secondary throttles also provide improved transient driveability response when used with large volume intake manifolds. Although it is also known that a long, low speed runner and a short high speed runner could be combined with a secondary throttle and a plenum throttle, as in U.S. Pat. No. 5,267,543, which is assigned to the assignee of the present invention, it is not known with such an arrangement to have secondary throttles operate upon the air flowing through both the high and low speed runners.
It is an advantage of the present invention that an intake system according to this invention will produce excellent combustion stability and torque at all engine speeds, while also providing enhanced tuning and cylinder filling at high engine speeds. Because the present system provides high tumble at idle and part throttle conditions, more exhaust gas recirculation (EGR) can be tolerated, thereby promoting reduction in the emission of oxides of nitrogen (NO.sub.x). Other advantages of the present invention will become apparent to the reader of this specification.